Such a mask may be incorporated into the bulb, or an added component fixed on the bulb-holder or on the reflector. In certain headlights, the mask is mounted on one or two vertical brackets extending between the top and/or bottom of the reflector and the region situated in front of the bulb, where they hold the mask.
It has been found that the presence of these brackets undesirably modifies the photometry of a light beam obtained using a reflector which is capable of generating by itself, that is to say without action of the sealing glass, a beam with a wide cut-off.
Examples of such automatic width-generating reflectors are described for example in the documents FR-A-2 609 148, FR-A-2 639 888 and FR-A-2 664 677 in the name of the applicant.
A known headlight has a bulb, and with a bulb filament and a direct light mask provided in front of the bulb also has two vertical brackets connecting the direct light mask to the upper and lower regions of a reflector in which the bulb is mounted. A width-generating reflector surface forms a European type dipping beam unit.
In this lamp, the bracket obstructs the passage of reflected rays directed towards it, and it turns out that, with the type of reflector considered, the occulted rays would cover an angular range for example from -2.degree. to +2.degree. in the beam formed. As a result of the occultation, a lack of light occurs in a fault zone which is slightly offset to the right, simply as a result of the reflective surfaces being, in a manner known per se, designed to offset at least part of the light slightly to the right with respect to the center of a reference projection screen.